The inheritance of traits from parent to offspring is a universal characteristic of life on earth, and has fundamental consequences for its inner workings, and for evolution. Recent results in the field of epigenetics have resurrected the once-discredited possibility that the environment of parents could have an effect on the phenotype of their offspring. Inheritance of acquired characters (ie passage of environmental information from one generation to the next) is often called Lamarckian inheritance, and demonstration of its existence would drastically alter how we think about evolution, and how human epidemiological studies are carried out. I have used a microarray approach to identify transgenerational effects of the paternal environment on offspring phenotype in mice, linking paternal low protein diet to cholesterol metabolism in offspring. Furthermore, we have shown that this information is carried in sperm. In this project I propose to systematically characterize the mechanism by which environmentally-directed traits are inherited in mice. We will carry out whole-genome analysis of epigenetic information carriers in sperm, thereby identifying diet-directed changes in the sperm epigenome. In addition, using an innovative approach based on in vitro fertilization, we will systematically identify epigenetic marks that persist after fertilization. These studies will have revolutionary impact on fields ranging from evolution to epidemiology.